The applicant of the present application has proposed an improved heat exchanger as an evaporator for a car air conditioner which satisfies the needs of reducing size and weight and enhancing performance (see Patent Document 1). In the improved heat exchanger, a plurality of heat exchange tube groups are arranged in a front-rear direction between upper and lower header tanks separated from each other in a vertical direction. Each heat exchange tube group consists of a plurality of heat exchange tubes which are arranged at predetermined intervals along the longitudinal direction of the header tanks and whose opposite end portions are connected to the corresponding header tanks. Each of the header tanks includes two header sections arranged in the front-rear direction and integrated together. Each of header tanks is composed of a first member which is formed of an aluminum brazing sheet and to which all the heat exchange tubes are connected; and a second member which is formed of an aluminum extrudate and which is joined to the first member so as to cover the side of the first member opposite the heat exchange tubes. A single heat exchange tube group is provided between each header section of the upper header tank and the corresponding header section of the lower header tank. The front header section of the upper header tank serves as a refrigerant inlet header section; the rear header section of the upper header tank serves as a refrigerant outlet header section; the front header section of the lower header tank serves as a first intermediate header section; and the rear header section of the lower header tank serves as a second intermediate header section. A refrigerant inlet is formed in one end portion of the refrigerant inlet header section, and a refrigerant outlet is formed in an end portion of the refrigerant outlet header section located on the same side as the end portion of the refrigerant inlet header section. The interiors of the refrigerant inlet header section, the refrigerant outlet header section, and the second intermediate header section are each divided into upper and lower spaces by means of a partition portion formed integrally with the corresponding second member. The upper and lower spaces within the refrigerant inlet header section communicate with each other via a communication hole formed in the partition portion at an end portion opposite the refrigerant inlet and the refrigerant outlet, as well as via a plurality of refrigerant-passage through holes formed in the partition portion at intervals in the longitudinal direction. The upper and lower spaces of the refrigerant outlet header section communicate with each other via refrigerant-passage through holes formed in the corresponding partition portion. Similarly, the upper and lower spaces of the second intermediate header section communicate with each other via refrigerant-passage through holes formed in the corresponding partition portion. Further, the space within the first intermediate header section and the lower space within the second intermediate header section communicate with each other via a communication portion provided in one end portion of the lower header tank with respect to the longitudinal direction thereof. In the heat exchanger, the second member is formed of an aluminum extrudate.
Incidentally, in order to improve the heat exchange performance of the heat exchanger described in Patent Document 1, the divided flow of refrigerant to all the heat exchange tubes must be controlled such that discharged-air temperature, or the temperature of air having passed through the heat exchanger, becomes uniform among different portions of the heat exchanger. In order to control the divided flow of refrigerant to all the heat exchange tubes, it is necessary to properly control the flow of refrigerant from the upper space to the lower space within the refrigerant inlet header section, the flow of refrigerant from the lower space within the refrigerant inlet header section to all the heat exchange tubes of the front heat exchange tube group, and the flow of refrigerant from the upper space within the second intermediate header section to all the heat exchange tubes of the rear heat exchange tube group. Such flow control can be effectively performed by means of forming the partition portions of the refrigerant inlet header section and the second intermediate header section to have a complicated shape, or forming flanges around the through holes of the partition portions of the refrigerant inlet header section and the second intermediate header section such that the flanges project toward the heat exchange tubes.
However, in the case of the heat exchanger described in Patent Document 1, since each second member having an integrally formed partition portion is formed of an aluminum extrudate, the partition portion can be formed only into the shape of a flat plate. In addition, since the through holes are formed by performing press working on the partition portion, it is impossible to form flanges around the through holes such that the flanges project toward the heat exchange tubes. Accordingly, in the case of the heat exchanger described in Patent Document 1, separate components must be provided in order to control the divided flow of refrigerant to all the heat exchange tubes such that discharged-air temperature, or the temperature of air having passed through the heat exchanger, becomes uniform among different portions of the heat exchanger. In this case, there arise problems that the number of components increases, and production work becomes troublesome.    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2006-183994